In conventional semiconductor devices, use is made of a lead frame 101 (see FIG. 7) when packaging a semiconductor chip (die). The lead frame 101 is obtained by forming a strip-shaped thin metal plate of superior mechanical strength, electrical conductivity, thermal conductivity and corrosion resistance, such as a Cu-based material or Fe-based material, into a desired shape by pressing work or an etching process. The lead frame 101 has die pad 102; a plurality of inner leads 103 extending toward the outer periphery of the die pad 102 with a prescribed spacing between them and the die pad 102; a tie bar 104 integrally connected to the inner leads 103; outer leads 105 connected to the inner leads 103 and extending toward the outer side of the inner leads 103; a side rail 106 to which the outer leads 105 are connected; and support bars 107 that support the die pad 102.
As illustrated in FIG. 8, the semiconductor device using the lead frame 101 has a semiconductor chip 115 fixedly secured on the die pad 102 (island) of the lead frame 101 via a bonding agent comprising solder or the like. Terminals (not shown) of the semiconductor chip 115 are connected to the inner leads 103 of the lead frame 101 by bonding wires 116 comprising gold wire or aluminum wire, etc., and the outer leads 105 of the lead frame 101 are lead out to the exterior. An assembly comprising at least the semiconductor chip 115, die pad 102, inner leads 103 and bonding wires 116 is sealed within a resin 117.
In a method of manufacturing such a semiconductor device, the semiconductor chip 115 is mounted on the bonding agent 119 after the bonding agent 119 is applied to the surface of the die pad 102 of the lead frame 101. This is followed by connecting the terminals (not shown) of the semiconductor chip 115 and the inner leads 103 of the lead frame 101 by the bonding wires 116, then leading the outer leads 105 of the lead frame 101 to the exterior and then sealing the assembly, which comprises at least the semiconductor chip 115, die pad 102, inner leads 103 and bonding wires 116, in the resin 117. This is followed by cutting off the tie bar 104 and side rail 106 and forming the outer leads 105, which extend from the resin 117, into the desired shape to thereby complete manufacture.
In order to improve the adhesion between the die pad 102 and resin 117 in a conventional semiconductor device, a technique in which the top and bottom surfaces of the die pad 102 are provided with dimples 118 and 120 beforehand at fabrication of the lead frame has been disclosed (see Patent Document 1).
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-A-9-92778 (FIGS. 1 and 2)